<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script>
			var radius=prompt("请您输入圆的半径：");
			alert("圆的半径等于："+(radius*radius*Math.PI));
		</script>
	</body>
</html>
